Recreational vehicle use has been increasing steadily in the U.S. for many years. Early travel trailers offered few amenities for travelers. To remedy this, bigger and heavier trailers were produced to provide more of the comforts of home. Taking advantage of this, more people spent more time travelling or simply living in their trailers. Manufacturers have responded to their demands for ever more comfortable trailers, further increasing the size and weight of the trailers. It is now unusual for a travel trailer to have only one axle, and more common to have two or more axles.
As homes, travel trailers are a series of compromises. Every aspect of a trailer must fit within the dimensions of existing roadways and comply with Department of Transportation regulations and guidelines. One basic difference between a house and a recreational vehicle trailer is the wheel and suspension system.
The trailer's suspension is designed to adapt and react to irregularities in the road surface. This permits the trailer body to remain relatively motionless in the vertical plane with respect to the road surface. This protects the trailer body from excessive shock, impact damage and vibration. However, those very qualities that serve to protect the trailer also permit the trailer to rock, roll and exhibit excessive motion when parked, due to the motion of trailer occupants.
Numerous devices have been designed to reduce the amount of motion experience by stationary trailers, including wheel chocks, wedge mechanisms, and frame jacks. Each of these concepts has its own set of disadvantages.
Wheel chocks are designed to bear tightly against the trailer's tires where they meet the ground. Optimally, the chocks should be used in pairs to prevent the trailer from rolling in either direction. However, while chocks are very good at preventing a trailer from rolling away, they are not able to eliminate much wheel rolling motion. On level ground, no matter how tightly one chock bears against a tire, the amount of control or stability is reduced by the amount of force applied by the other chock. It is virtually impossible to place both chocks in position tightly at the same time, due to tire pressure and external forces. Chocks permit a significant amount of motion. In addition, chocks are bulky and can be quite heavy due to their strength requirements.
Wedge mechanisms are designed to act as vertically-oriented chocks that are connected together and are used with tandem-axle trailers. A top wedge bridges the gap between the two tires above the tires' centerline. A lower wedge is symmetrically oriented below the centerline of the tires. Each wedge is too broad to fit between the tires at the narrowest point. Thus, when the wedges are linked to each other, drawing them closer together acts to frictionally jam the tires in place. However, trailer tires are very flexible in their tread, by necessity. Thus, the frictional interference between the tires and wedges will not prevent the tire tread from flexing due to the motion of a trailer occupant. Further, the strength and dimensional requirements of the wedges and accompanying tensioning mechanism means that this system is bulky and heavy.
Frame jacks are another option. The jacks are positioned between the ground and the trailer's frame to slightly lift the trailer and decrease or eliminate the role of the wheels and suspension while the trailer is parked. Jacks are very effective in reducing the vertical motion of a trailer, but they must be extended carefully to prevent excessive trailer frame twist. Further, jacks require a solid surface or very firm soil condition to prevent their sinking into the ground. This often requires a ready supply of heavy timbers or other lumber to distribute the load from the jack, or to allow a short jack to reach the trailer frame. This is also a heavy, bulky solution. Thus, what is needed is an effective solution to eliminate undesirable motion in stationary trailers that is lightweight and easy to store.